BEIJING, March 28 (Reuters) - A former aide to China's retired domestic security chief Zhou Yongkang was sacked on Thursday after authorities opened a corruption probe, state media said, the latest move targeting associates of Zhou, who is also under investigation for graft.

The official Xinhua news agency said Ji Wenlin had been removed from his post as a vice governor of the southern island province of Hainan.

The ruling Communist Party's anti-corruption watchdog announced in February that Ji was being investigated for suspected serious breaches of party discipline and the law, the usual euphemism it uses for graft.

The government has given no other details and it has not been possible to reach Ji for comment. Sources have told Reuters that Zhou has been put under virtual house arrest.

President Xi Jinping has launched a sweeping crackdown on corruption since taking power, warning corruption is a threat to the Communist Party's survival.

Ji worked with Zhou when Zhou was land resources minister in the late 1990s. He then followed Zhou to Sichuan province and became one of his secretaries when Zhou was provincial party boss, Ji's official resume shows.

The two also worked together in the Ministry of Public Security in the early 2000s. In late 2010, Ji was shifted to Hainan province, known in China for its pristine beaches and resorts.

The party also fired Yao Mugen, the vice governor of the eastern province of Jiangxi, for "suspected severe violations of discipline", state news agency Xinhua reported on Friday.

The Xinhua report, which cited the ruling party's central Organisation Department, said his case was handled "in line with procedures". The term "discipline violation" is also generally used to denote corruption.

Several of Zhou's political allies have been held in custody and questioned over corruption, including former Vice Minister of Public Security Li Dongsheng and Jiang Jiemin, who was the top regulator of state-owned enterprises for just five months until September.

It is unclear if the government will put Zhou on trial and risk embarrassing public revelations about China's elite, potentially undermining confidence in the party.

Zhou was a patron of former high-flying politician Bo Xilai, who was jailed for life in September for corruption and abuse of power in the worst political scandal since the 1976 downfall of the Gang of Four led by the widow of former leader Mao Zedong at the end of the Cultural Revolution.

Zhou retired in 2012. He was last seen at an alumni celebration at the China University of Petroleum on Oct. 1.